Cardiovascular effects of injections of vasopressin into the nucleus tractus solitarius in conscious rats.

The effects of injections of arginine vasopressin (AVP) into the nucleus tractus solitarius (NTS) on mean arterial pressure (MAP), heart rate (HR) and plasma concentrations of noradrenaline and adrenaline were investigated in conscious, unrestrained rats. Injection of 2 ng AVP into the NTS significantly increased MAP but not plasma catecholamine concentrations, while injection of 10 ng AVP significantly increased MAP and plasma noradrenaline and adrenaline levels. Neither dose of AVP produced any change in HR. The vehicle did not affect MAP, HR or plasma catecholamine levels. Injection of a specific pressor antagonist of AVP, d(CH2)5Tyr-(Me)AVP (10 ng), did not change MAP, HR or plasma noradrenaline or adrenaline levels. These results suggest that the NTS is a central site of the pressor action of AVP. However, since the injection of the AVP antagonist did not reduce MAP or plasma noradrenaline or adrenaline levels, it suggests that AVP does not act tonically at the NTS to influence sympathoadrenal outflow.